1. Field of the Invention
The present invention relates to an ion source for generating a ribbon-like ion beam (may be referred to as sheet-like or belt-like, the same holds for the following description). The ion beam dimension in the Y direction in a plane substantially orthogonal to a traveling direction is larger than the dimension in the X direction substantially orthogonal to the Y direction, an ion implantation apparatus including the same ion source, and an ion implantation method in the ion implantation apparatus.
2. Description of the Related Art
FIG. 1 shows an example of a ribbon-like ion beam 2 whose dimension WY in the Y direction in a plane substantially orthogonal to the traveling direction Z is larger than the dimension WX in the X direction substantially orthogonal to the Y direction.
In JP-A-2002-334662 (Paragraph 0002-0012, FIG. 12), a Bernas-type ion source is described in which filaments and a reflecting electrode are opposed across a longitudinal direction of an ion extraction slit, and in a direction along an axis connecting these (that is, along the longitudinal direction of the ion extraction slit), an applied magnetic field is described. By setting the longitudinal direction of the ion extraction slit of this ion source as the Y direction, it is possible that a ribbon-like ion beam with a larger dimension in the Y direction as described above may be generated.
To realize uniform ion implantation into, for example, a large-sized target by using the above-described ion source, it is necessary that the dimension of the ribbon-like ion beam to be generated (extracted) from the ion source is increased and the uniformity of the beam current density distribution in the Y direction is improved. Therefore, it is necessary to increase the dimension in the Y direction of a plasma generating vessel of the ion source and improve the uniformity of the plasma density distribution in the Y direction in the plasma generating vessel.
However, if the plasma generating vessel becomes larger, the plasma density distribution in the plasma generating vessel inevitably becomes nonuniform, so that it is difficult to extract an ion beam with a uniform beam current density distribution in the Y direction.
If it is attempted to perform control to make uniform the plasma density distribution in the plasma generating vessel by some method, in a related ion source, a magnetic field is applied along the Y direction and the influence of the magnetic field spreads over in the Y direction, so that it is difficult to partially control the plasma density in the Y direction, and therefore, it is difficult to improve the uniformity of the plasma density distribution in the Y direction. In other words, the magnetic field along the Y direction makes it difficult to control the plasma density distribution in the Y direction. However, if the application of the magnetic field is stopped, the electron confinement by the magnetic fields becomes impossible, so that the plasma generation efficiency lowers.